I never do that, at least not for the sake of just being snoopy/nosey. Like others have mentioned if I know someone well I will just open a cupboard or the like to get something I need and I will look at the pics on the walls, knick knacks on shelves etc... but I don't open anything up just to poke around.

I try my best to live by my motto "do onto others as you would want done unto you"